Synergistic Mn-Cr Co-doping in Na₃V₂(PO₄)₂O₂F Promising Cathode: Unlocking Superior Performance for Next-Generation...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium vanadium fluorophosphate (Na₃V₂O₂(PO₄)₂F, NVOPF) is a promising NASICON cathode material with high voltage and theoretical energy density.
• Limitations include poor electronic conductivity and low practical energy density, hindering commercialization.

Purpose of the Study:

• To enhance the electrochemical performance of NVOPF by addressing its conductivity and ion diffusion limitations.
• To investigate the effects of Mn and Cr co-doping on the NASICON structure and sodium-ion transport properties.

Main Methods:

• A one-pot solvothermal method was employed for the synthesis of Mn and Cr co-doped NVOPF.
• Density Functional Theory (DFT) calculations were used to analyze lattice distortion and ion diffusion.
• Electrochemical testing, including cycling performance, rate capability, and full-cell evaluation, was conducted.

Main Results:

• Optimized Na₃V_1.9Mn_0.095Cr_0.005O₂(PO₄)₂F (NVMC-95) exhibited improved ionic and electronic conductivity.
• NVMC-95 demonstrated excellent cycling stability (94% retention after 500 cycles at 1C) and rate capability (87 mAh g⁻¹ at 20C).
• Full-cell tests against hard carbon showed high operating voltage and sustained capacity over 100 cycles.

Conclusions:

• Mn/Cr co-doping effectively enhances Na⁺ transport, reduces impedance, and improves the kinetics of NVOPF cathodes.
• The synergistic effect of co-doping leads to a stabilized NASICON structure with extended cycle life.
• This work presents a viable strategy for developing durable and high-performance NASICON-type cathode materials for sodium-ion batteries.